Three phase transformers are used on three phase energy systems either as security - isolation type transformer or step up -down transformer, in some cases step-up and step down transformers can be produces as auto transformer for reducing the price. Nominal power Isolation type or auto type Input-output voltage and current values according to duty factor Input - output connection types ( delta - star etc ) Galvanic isolation Input - output voltage steps Input-output connection materials Isolation class Metal enclosure and ventilation Mounting type ( horizontal - vertical ) ... Etc Guven-is determines these technical specifications by communicating directly to the customer before designing process in order to avoid any problem. When every detail is clear a sample transformer is produced and tested by guven-is and submitted to the customer for the final approving before the ordering. Http://en.Guvenisregulator.Com.Tr/userfiles/files/3%20phase%20transformer%20eng(1).Pdf